This invention relates to the preparation of novel polymeric materials by the chemical modification of polyolefins, olefin copolymers, and other polymeric materials with a structure containing saturated aliphatic carbon atoms. The resulting modified polymers are highly suitable for use in coating, adhesive, and packaging applications.
More particularly, this invention relates to the chemical combination of a polyolefin polymer or copolymer with one or more non-polymeric organic compounds having the generalized structure R-X, where R is a saturated linear, branched, or cyclic aliphatic hydrocarbon residue containing at least six carbon atoms, and X is a polar functional group which is a member of the series comprising the following groups:
Hydroxyl (--OH); PA1 carboxyl (--COOH); PA1 amide (--CONH.sub.2); PA1 mono- or disubstituted amide PA1 (--CONHR.sub.1 or --CONR.sub.1 R.sub.2), where the substituents R.sub.1 and R.sub.2 are the same or different lower alkyls containing one to four carbons; PA1 Amino (-NH.sub.2); PA1 mono- or disubstituted amino PA1 (--NHR.sub.1 or --NR.sub.1 R.sub.2), where the substituents R.sub.1 and R.sub.2 are the same or different lower alkyls containing one to four carbons; ##STR1## where the substituents R.sub.1, R.sub.2, and R.sub.3 are lower alkyls containing one to four carbon atoms; PA1 Sulfonic acid (--SO.sub.3 H); PA1 hydrogen sulfate (--OSO.sub.3 H); PA1 Dihydrogen phosphate (--OPO.sub.3 H.sub.2). PA1 Carboxylate (--COO.sup..crclbar.); PA1 sulfonate (--SO.sub.3.sup..crclbar.); PA1 singly charged sulfate (--OSO.sub.3.sup..crclbar.); PA1 singly or doubly charged phosphate (--OPO.sub.3 H.sup..crclbar. or --OPO.sub.3.sup..crclbar.); PA1 ammonium (--N.sup..sym. R.sub.1 R.sub.2 R.sub.3); where the substituents R.sub.1, R.sub.2 and R.sub.3 are hydrogens or lower alkyls containing one to six carbons; PA1 Sulfonium (--S.sup..sym. R.sub.1 R.sub.2), where the substituents R.sub.1 and R.sub.2 are the same or different lower alkyls containing one to six carbons; PA1 Phosphonium (--P.sup..sym. R.sub.1 R.sub.2 R.sub.3), where the substituents R.sub.1, R.sub.2 and R.sub.3 are the same or different lower alkyls containing one to six carbon atoms.
and
The group X may also bear one or more units of positive or negative charge, as in the case of the following groups:
And
In the case of such charged groups, it should be understood that an ion of opposite charge is simultaneously present, such as a sodium ion in the case of a carboxylate or sulfonate group, and a halide ion in the case of an ammonium, sulfonium, or phosphonium group.
It is further contemplated that the co-reactant R-X may contain heterocyclic rings as a part of the structure of R, in addition to the essential aliphatic hydrocarbon group or groups. Furthermore, it should be understood that more than one group of type R, and/or more than one group of type X, may be present per molecule of co-reactant R--X.
Many compounds of the type R--X as described hereinbefore, particularly those having a single group of type R and a single group of type X, are referred to as `surfactants` owing to their surface-active properties.
This invention consists of effecting the chemical combination of the polymeric polyolefin reactant and the non-polymeric co-reactant (R--X), preferably in the presence of one or more sensitizing additives, to ultraviolet or visible radiation of appropriate wavelength.
The term `sensitizer` is applied to reagents which are capable of absorbing ultraviolet and/or visible radiation and, following such photochemical excitation, of initiating or accelerating chemical reactions which lead to chemical combination of the polymer and co-reactant. Preferred additives are those which are known to initiate free-radical reactions, such as photopolymerization and photooxidation.
While the mechanism of the photosensitized chemical modification process is not presently understood in detail, it is believed that the excited state of the photosensitizer undergoes subsequent processes (such as unimolecular decomposition, hydrogen abstraction, or energy transfer) which lead directly or indirectly to the formation of free-radical intermediates. Free radicals derived from the polymer combine with other free radicals derived from the co-reactant, so that polar groups (X) derived from the co-reactant became chemically bonded to the polymer molecules.
The formation of crosslinked polymers by processes involving the formation and interaction of free-radical intermediates is known in the prior art. In such processes, a crosslink between polymer chains is formed as a result of the combination of polymeric radicals. Typically, this is accomplished by heating a mixture of a polymer and an organic peroxide to a temperature at which the peroxide decomposes to free radicals.
The formation of graft copolymers by free-radical processes is also known in the prior art. In such processes, a polymeric radical is formed, and undergoes an addition reaction with the reactive carbon-carbon double bond of a vinyl monomer, such as styrene or methyl methacrylate; the resulting radical then adds further units of vinyl monomer by successive radical addition reactions. Typically, such a graft copolymerization is accomplished by heating a mixture of a polymer, a vinyl monomer, and an organic peroxide to a temperature at which the peroxide decomposes to yield free radicals.
Likewise, the preparation of physical blends of polymers with certain types of non-polymeric additives of the type R--X is known in the prior art. Typically, such additives are employed so as to confer antistatic properties or to aid in the dispersion of particulate materials in polymers or polymer solutions.
The use of sensitizing additives which facilitate the initiation of certain types of free-radical reactions is also known in the prior art. For example, irradiation of a mixture of a vinyl monomer and a sensitizing additive is known to lead to photopolymerization.